Ovarian cancer is the sixth most common cancer in women, accounting for 6% of all female cancers. It ranks fifth as the cause of cancer death in women. The American Cancer Society predicts that there will be about 23,100 new cases of ovarian cancer in this country in the year 2000 and about 14,000 women will die of the disease. Because many ovarian cancers cannot be detected early in their development, they account for a disproportionate number of fatal cancers, being responsible for almost half the deaths from cancer of the female genital tract; more deaths than any other reproductive organ cancer.
Most patients with epithelial ovarian cancer, the predominant form, are asymptomatic in early-stage disease and usually present with stage III or IV disease. Their five-year survival is less than 25%, with lower survival among African-American women. The minority of patients discovered with early-stage disease have a five-year survival rate of 80%-90% (Parker, S. L. et. al. Cancer statistics, 1997. CA 1997: 47: 5-27).
In the absence of a family history of ovarian cancer, lifetime risk of ovarian cancer is 1/70. Risk factors include familial cancer syndromes (risk of up to 82% by age 70 in women with hereditary breast/ovarian syndrome); family history (1.4% lifetime risk with no affected relatives, 5% with one affected relative, 7% with two affected relatives; Kerlikowske, K. et. al. Obstet Gynecol (1992) 80: 700-707) nulliparity; advancing age; obesity; personal history of breast, endometrial, or colorectal cancer; fewer pregnancies; or older age (>35 years) at first pregnancy. However, 95% of all ovarian cancers occur in women without risk factors. Use of hormonal contraceptives, oophorectomy, and tubal sterilization reduce risk of ovarian cancer (Kerlikowske, K. et. al. Obstet Gynecol (1992) 80: 700-707; Grimes, D. A. Am J. Obstet. Gynecol. (1992) 166: 1950-1954; Hankinson, S. E. et. al. (1993) JAMA 270: 2813-2818) however, even bilateral oophorectomy may not be completely effective in preventing ovarian cancer.
Treatment of ovarian cancer consists largely of surgical oophectemy, anti-hormone therapy, and/or chemotherapy. Although many ovarian cancer patients are effectively treated, the current therapies can all induce serious side effects which diminish quality of life. Deciding on a particular course of treatment is typically based on a variety of prognostic parameters and markers (Fitzgibbons et al., 2000, Arch. Pathol. Lab. Med. 124:966-978; Hamilton and Piccart, 2000, Ann. Oncol. 11:647-663), including genetic predispostion markers BRCA-1 and BRCA-2 (Robson, 2000, J. Clin. Oncol. 18:113-118).
The identification of novel therapeutic targets and diagnostic markers is essential for improving the current treatment of ovarian cancer patients. Recent advances in molecular medicine have increased the interest in tumor-specific cell surface antigens that could serve as targets for various immunotherapeutic or small molecule strategies. Antigens suitable for immunotherapeutic strategies should be highly expressed in cancer tissues and ideally not expressed in normal adult tissues. Expression in tissues that are dispensable for life, however, may be tolerated. Examples of such antigens include Her2/neu and the B-cell antigen CD20. Humanized monoclonal antibodies directed to Her2/neu (Herceptin®/trastuzumab) are currently in use for the treatment of metastatic breast cancer (Ross and Fletcher, 1998, Stem Cells 16:413-428). Similarly, anti-CD20 monoclonal antibodies (Rituxin®/rituximab) are used to effectively treat non-Hodgkin's lymphoma (Maloney et al., 1997, Blood 90:2188-2195; Leget and Czuczman, 1998, Curr. Opin. Oncol. 10:548-551).
Potential immunotherapeutic targets have been identified for ovarian cancer. One such target is polymorphic epithelial mucin (MUC1). MUC1 is a transmembrane protein, present at the apical surface of glandular epithelial cells. It is often overexpressed in ovarian cancer, and typically exhibits an altered glycosylation pattern, resulting in an antigenically distinct molecule, and is in early clinical trials as a vaccine target (Gilewski et al., 2000, Clin. Cancer Res. 6:1693-1701; Scholl et al., 2000, J. Immunother. 23:570-580). The tumor-expressed protein is often cleaved into the circulation, where it is detectable as the tumor marker, CA 15-3 (Bon et al., 1997, Clin. Chem. 43:585-593). However, many patients have tumors that express neither HER2 nor MUC-1; therefore, it is clear that other targets need to be identified to manage localized and metastatic disease.
While industry and academia have identified novel sequences, there has not been an equal effort exerted to identify the function of these novel sequences. The elucidation of a role for novel proteins and compounds in disease states for identification of therapeutic targets and diagnostic markers is essential for improving the current treatment of ovarian cancer patients. Accordingly, provided herein is a molecular target for therapeutic intervention in ovarian and other cancers. Additionally, provided herein are methods that can be used with this target in diagnosis and prognosis of ovarian cancer.
The GPR64 protein has been implicated in certain cancerous conditions, e.g. ovarian cancer, Ewing's sarcoma, and uterine cancer. Antibodies useful for diagnosis, prognosis, and effective treatment of cancer, including metastatic cancer, would be desirable. Accordingly, provided herein are compositions and methods that can be used in diagnosis, prognosis, and therapy of certain cancers.
GPR64 (also referred to in the literature as Ov1 and HE6, and sometimes referred to in this document and figures and OAM6) is an orphan G-protein coupled receptor with a large, heavily glycosylated N-terminal extracellular domain.
GPR64 has been cloned by Osterhoff et al., (1997, DNA AND CELL BIOLOGY 16:379-389) as an epididymus-specific G-protein coupled receptor (GPCR).
Gene expression profiling as described in U.S. Ser. No. 10/173,999, filed Jun. 17, 2002 (which is hereby incorporated by reference in its entirety), and the Examples contained herein, indicates that GPR64 is up-regulated in ovarian cancer tissue relative to normal tissue.
A bioinformatics analysis of the GPR64 gene sequence based on publicly available database information suggests that the protein product contains a signal sequence, a large extracellular domain (619 amino acids), seven transmembrane domains and is predicted to locate to the plasma membrane and function as a G-protein coupled receptor. This makes GPR64 an attractive target for therapeutic antibodies.